The present embodiments relate to Single Photon Computed Tomography (SPECT). The reconstruction of a SPECT image is often difficult because the data is characterized by small signal rates and low signal-to-noise ratio. For SPECT imaging, the count rate is limited by the amount of a radionuclide (i.e., radioactive substance or radiotracer) that can be administered without harming the patient. Some radionuclides (e.g., Lu-177, I-123, Ga-67 and Y-90) have complicated energy spectra. For radionuclides with complicated spectra, the inaccurate model of the image formation process in iterative reconstruction may degrade the SPECT image. Multi-energy reconstruction may be used to benefit from the complicated energy spectra. Image blurring may still result due to degradation of resolution in the image formation process.
A SPECT image does not necessarily provide structural information. Thus, a SPECT image is often evaluated with the help of an adjacent structural image. Computed tomography (CT) may be used for the structural image. In multi-modality imaging, the CT data may be used as part of the SPECT reconstruction, such as by reconstructing separately for different types of tissue or zones. The zonal reconstruction may improve accuracy or resolution. When zonal reconstruction is used for radionuclides with complicated energy spectra (e.g., I-123 and Lu-177), due to the inaccurate image formation model, enhanced resolution does not necessarily lead to improved quantitative accuracy. In fact, resolution enhancement may reduce the quantitative accuracy. There are no SPECT reconstruction approaches that simultaneously address (a) the inaccuracy of the image formation process for complicated energy spectra and address (b) image blurring due to degradation of resolution.